The big US broadcasters are primarily leaning on legal action to shut down Aereo's antenna-based streaming TV service, but what if the startup prevails in court? Apparently, the media giants aren't too worried; they have some backup plans. The Wall Street Journal claims that CBS is considering a subscription-based video service of its own that would offer both live and on-demand shows for a few dollars per month. While it would still include ads, there might also be an option to pay for Showtime's premium programming.The big providers may not decide to fight Aereo in the marketplace, though. Other options include lobbying Congress for anti-Aereo legislation or even pulling content from over-the-air broadcasting. This last option may be impractical -- it could limit the content that affiliates can offer, hurting both local stations as well as viewers that can't afford (or simply don't want) pay TV. The operators haven't locked down what they plan to do, but Aereo hasn't discussed a failsafe of its own. If it loses its court battle, the networks may not have to lift a finger.